Globin gene transfer for treatment of the β-thalassemias and sickle cell disease

The β-thalassemias and sickle cell disease are severe congenital anemias that are caused by mutations that alter the production of the β chain of hemoglobin. Allogeneic hematopoietic stem cell (HSC) transplantation is curative, but this therapeutic option is not available to the majority of patients. The transfer of a functional globin gene in autologous HCSs thus represents a highly attractive alternative treatment. This strategy, simple in principle, raises major challenges in terms of controlling the expression of the globin transgene, which ideally should be erythroid specific, differentiation-stage restricted, elevated, position independent, and sustained over time. Using lentiviral vectors, we have demonstrated that an optimised combination of proximal and distal transcriptional control elements permits lineage-specific, elevated expression of the β-globin gene, resulting in therapeutic hemoglobin production and correction of anemia in β-thalassemic mice. Several groups have now confirmed and extended these findings in various mouse models of severe hemoglobinopathies, thus generating enthusiasm for a genetic treatment based on globin gene transfer. Furthermore, globin vectors represent a general paradigm for the regulation of transgene function and the improvement of vector safety by restricting transgene expression to the differentiated progeny within a single lineage, thereby reducing the risk of activating oncogenes in hematopoietic progenitors. Here we review the principles underlying the genesis of regulated vectors for stem cell therapy